Isotope separators



2 Sheets-Sheet 1 Filed Nov. 18, 1954 INVENTOR Joseph Slepion ATTORNEYJune 26, 1956 J. SLEPIAN ISOTOPE SEPARATORS 2 Sheets-Sheet 2 Filed Nov.18, 1954 Circumferential Electric Field Direction of Magnetic Force onCurved Current HeV I Fig.5.

United States Patent ISOTOPE SEPARATORS' Joseph. Slepian, Pittsburgh,Pa.

Application November 18, 1954, Serial No. 469,784

21 Claims. (Cl. 250-413) My invention relates to isotope separators, andhas particular relation to electromagnetic isotope separators, byoperation of which substantial quantities of material may be obtained.

The basic problem which has arisen in the development of the so-calledatomic or nuclear industry has concerned itself with the separation ofisotopes, and particularly the isotopes of uranium and lithium. To beuseful, the separation must make available large quantities of thematerial consisting purely of a certain isotope. To an extent, thisproblem has been solved by the provision of separators in which theseparation is effected by gas difiusion. Gas diffusion separators,however, demand enormous quantities of power.

It is, accordingly, a general object of my invention to provideapparatus for separating isotopes, the power requirements of which shallbe relatively moderate as compared with gas difiusion separators.

My invention in its broader aspects is based on the realization that theelectromagnetic mass separator, acting on the isotopes in ionized form,offers means for obtaining substantial quantities of separate isotopeswhile consuming substantially less power than for gas difiFusionseparators. Heretofore, the process of electromagnetic mass separationhas been encountered in mass spectrographs. But, in mass spectrographs,the quantity of material transmitted per unit time by the current whichfiows is very small, there being no space-charge neutralizing electrons,and, while such spectrographs are suitable for measurement purposes,they are not useful for the purpose of obtaining substantial quantitiesof separated isotopes, because with space-charge neutralizing electronsabsent, they are unable to yield appreciable quantitles of material in areasonable time interval.

It is, accordingly, another general object of my invention to provide anelectromagnetic mass separator, acting on the ions of the isotopes, withspace-charge neutralizing densities of electrons, for obtainingsubstantial quantities of separate isotopes of an element in arelatively short time interval.

An electromagnetic mass separator with Whichthis object may beaccomplished must meet two basic conditions. First, a su-ificient numberof ions must be deposited per unit time on collectors from which thecollected mass may be readily removed to provide a substantial mass orquantity of the material when the apparatus operates over a. shorttimeinterval. Second, the material must be distributed over the collector,so that there is a substantial enrichment during each operation of theapparatus, or the isotope to be separated in a predetermined region ofthe collector.

It is, accordingly, a specific object of my invention to provide anelectromagnetic mass separator including a source of ions capable ofdelivering a substantial quantity of material per unit time in which alarge proportion of the ions and of electrons shall flow to a collectorfrom which the material may be readily removed.

2,752,503 Patented June 26, 195i;

It is an ancillary object of my invention to provide an electricdischarge device including a source of ions and electrons in which theflow of the ions shall be so controlled that they are deposited inpredetermined regions of the device.

Another specific object of my invention is to provide an electromagneticmass separator in which the ions and electrons shall be so distributedover the collector that during each operation of the apparatus thereshall be a substantial enrichment of the isotope to be separated inpredetermined regions of the collector.

An incidental object of my invention is to provide a novel arc dischargedevice particularly for producing a discharge rich in ions.

The electromagnetic separator to which my invention relates includes agenerally cylindrical. vessel having conductive bases andcircumferential walls, the bases capable of being insulated from thecircumferential walls. This vessel is maintained in a very high vacuum,less than micron, and at its center an arc is produced which carriessubstantial current, amperes or more, made up principally of electronsfrom the cathode, and to a smaller extent, of ions of the material fromthe anode and a space-charge neutralizing density of electrons also fromthe anode.

The bases of the vessel may be made up of a number of insulated sectionswhich may be at two or more different. potentials. Among these sectionsare rings of small diameter coaxial with the are. A high magnetic fieldis impressed longitudinally on the cylindrical vessel and electricfields are impressed within the vessel between electrodes within thevessel. Usually, also, a negative potential is impressed on the rings.

My invention arises from the discoveries first, that with a field ofrelatively low intensity impressed in the region of, the are, forexample by impressing a negative potential on the rings, the ions of theisotopes to be separated are projected with space-charge neutralizingelectrons in substantial quantities into the evacuated space surroundingthe arc, and, second, that effective separation of the isotopes may beproduced by impressing in this space. circumferential fields of constantpolarity; that is, fields produced by direct current potentials. Theprojection of substantial quantities of ions in the evacuated spaceoccurs because under the action of the relatively low electric field andthe magnetic field impressed, the discharge from the arc into the spaceincludes'not only ions, but electrons which are charged oppositely, andsupply a charge per unit volume equal and-opposite to that of the ions.Thus, the space charge produced by the ions of the isotopes within thespace is effectively neutralized, by that of the electrons, and the ionsand the equally and oppositely space-charged electrons flow into thespace in substantial quantities.

This motion of the electrons accompanying the ions outwardly is inapparent contradiction to the direction ofi the radial electric field,which is set so that it urges the ions outwardly and the electronsinwardly. Nevertheless, the electrons do move against the opposingradial electric field, the energy for this motion being obtained frominteractions with the positive ions. These interactions are notcompletely describable as collisions, but have properties similar tocollisions, in that the energy given to the electrons is randomlydirected.

The electrons are readily displaced in the direction of the magneticfield, and the random collisionswith the ions produce rapid reversals inthe up and down motion (that is, the motion axially to the cylinder) ofthe electrons. The electrons cannot escape because of thepotential whichis applied to the ring-shaped upper and lower electrodes bounding themagnetic field, and they acquire a random energy equal to a large partof the total energy of the positive ions.

Because of the smallness of mass of the electron, the electron will havea random velocity in the direction of the magnetic field several hundredtimes the velocity of the ion.

The electron velocity in the directions perpendicular to the magneticfield is also large, since these velocities are random to, coming fromthe same collisions with positive ions. But, in these directions,because of the low mass of the electron, the path of the electron isbent into small nearly closed curves by the action of the magneticfield.

While the electrons move rapidly up and down but do not escape becauseof the negative potential 'on the ring electrodes, a small number ofpositive ions escape at the ring electrodes, but their mass is 'sogreat, they form a space-charge there so that a sheath forms there whichseparates the negative potential on the ring electrodes, from the lower(less negative) potential of the space adjacent. In this lower (lessnegative) potential space, the electrons circulate up and down (axially)with high velocities past the ions, and in the directions perpendicularto the magnetic field, they circulate with similar high velocities butin tight smal spirals, and these spirals are open just enough so thatthe electrons accompany the ions in their motions.

The ions themselves acquire a random energy through this interchangewith the electrons. Their random energy is equal to that of theelectrons and has a large part of their mean energy. Hence, if theelectrical field is largely radial, only a modest enrichment of parts ofthe deposit is obtainable because of the large proportion which therandom motion of the ions is to the mean motion. My observations duringmore than ten years of the motion of ions and electrons in magneticfields completely confirm this.

In the practice of my invention, the circumferential electric fields areset up between two or more radial sets of electrodes or slats betweenwhich D. C. potentials are impressed. These radial electrodes or slatsare set with one end as near to the are as is practicable, and with theother end at the extreme outer end of the vacuum vessel. The initialradial electric field extends from the are out to the inner edge of theradial electrodes, and is applied by impressing the negative potentialto the inner rings of the upper and lower plates, the positive end beingconnected to the anode of the arc. inner edges of the radial slats.

A direct potential is applied between the alternate radial electrodes.This potential is in accordance with the preferred practice of myinvention, independent of The rings extend to the positive ions appearsjust at the surface of the negative electrode, and a space charge ofnegative electrons appears at the positive electrode, and these thinspace charges limit the electric field in the space between theelectrodes to a little more than that corresponding to Hv, where v isthe mean radial velocity of the ions at any point, and H is themagnitude of the magnetic field.

I shall say more about this circumferential field later. At this stage,it is enough to say that the circumferential electric field actsdifferentially upon the ions, and that the lighter ions (with electrons)are moved toward the negative plate, and the heavier ions (withelectrons) are moved toward the positive plate. They precipitate uponthe cylindrical boundary and the upper and lower plate boundary, and onthe radial plates. From these various portions of plates, the materialmay be removed after all the deposition is done. The parts next to thepositive plates are richer in the heavier ion, and the parts next to thenegative plates are richer in the lighter ion.

The novel features that I consider characteristic of my invention areset forth generally above. The invention itself, both as to itsorganization and its method of operation, together with additionalobjects and advantages thereof, will be understood from the followingdescription of specific embodiments when read in connection with theaccompanying drawings, in which:

Figure 1 is a view partly in side elevation and partly in sectionshowing an embodiment of my invention;

Fig. 2 is a view in section taken along lines IIII of Fig. 1;

Fig. 3 is a fragmental view in section of the electrodes used in thepractice of my invention;

Fig. 4 is a diagrammatic view showing the trajectories of the ions inthe practice of my invention;

Fig. 5 is a diagrammatic view showing the relationship between theforces on the ions in the practice of my invention;

Fig. 6 is a diagrammatic view illustrating a modification of myinvention;

Fig. 7 is a diagrammatic view showing another modification of myinvention;

Fig. 8 is a diagrammatic view showing still another modification of myinvention; and

Fig. 9 is a diagrammatic view of a further modification of my invention.

The apparatus shown in Figs. 1 and 2 includes a vacuum chamber 11 whichis connected to a system of vacuum pumps (not shown) through an exhausttube 13 and the potential between the rings and the arc electrode;

that is, the radial electrodes or slats float electrically relative tothe arc electrodes. This potential on the radial slats sets up twooppositely directed circumferential fields, which would draw currentsthrough the mass of ions and electrons brought up to the radialelectrodes by the initial radial electric field. These currents are ofsuch a sign that they cause the ions and electrons to be accelerated bythe uniform magnetic field outwardly on one side of the negative plates,and inwardly on the other side of the negative plates. The ions andelectrons then proceed outwardly in the alternate spaces between theplate electrodes. In the other alternate spaces between the plates, theions and electrons are not projected out: wards and these spaces may, inaccordance with the preferred practice of my invention, be reduced tonearly zero thickness, although, in accordance with the broader aspectsof my invention, they may be given any finite thickness.

The ions enter the circumferential fields with a mean velocity (which isnearly radial) and a random velocity, which nearly equals the radialmean velocity.- The currents which are drawn to the plates by the D. C.potential between them is limited, since a space charge of is capable ofbeing evacuated so that the pressure within this chamber is less than 1micron. The chamber 11 is of generally circularly cylindrical formhaving conducting bases 15 and 17 and a wall 19, the bases beingprovided with centrally disposed insulator inserts 21 and 23, and thewall 19 being provided with insulator inserts 25 and 27 and with anopening 29 into which the exhaust tube 13 is sealed. The vacuum chamberis preferably grounded.

Through the centrally disposed insulator inserts 21 and 23, electrodeholders 31 and 33 are passed. The lower holder 31 is dimensioned toreceive the positive electrode 35 which emits the ions, and thespace-charge-neutralizing electrons, and the upper holder 33 isdimensioned to receive the negative electrode 37. The holders areprovided with suitable facilities (not shown in detail) for connectionto a power supply. This supply must be adequate to produce an arebetween the electrodes 35 and 37 and must be suitably regulated toassure that the arc is properly maintained.

The negative electrode 37 may be a cored carbon made by manufacturers ofsuch electrodes in the United States, such as National Carbon Company ofCleveland, Ohio. It is a carbon rod 41 (Fig. 3), with its center drilledout, and having within it a core of oxides of the rare metal earths 173.Other electrodes may be used, however. All that is required is that itserve as a source of electrons; that is, as a cathode of an arcsupplying large currents of the order of amperes of electrons.

From each of the inserts 21 and 23 in the bases, a conducting ring 45and 47 is suspended. A conductor 49 and 51 is sealed through each insertand includes facilities (not shown in detail) for impressing a potentialbetween the conducting rings and the electrode holders. From each of thebases 15 and 17, a plurality of conductors 61 and 63 and 61 and 63, inthe form of segments of a circular arc, are suspended by studs 65. Theconducting segments 61 and 63 extending from each half of each baseoverlap. The studs 65 by which the segments are suspended are ofinsulating material, so that the segments may be insulated from thebases.

From the circumferential walls, a plurality of overlapping circularlycylindrical sections 67 and 69 are suspended. These sections 67 and 69are also mounted from insulating studs (not shown) but are themselvesconducting. The sections 67 and 69 may float electrically, in whichevent each respective plate 67 or 69 nearest the radial plates 71through 77 takes on a potential near the potential of the nearest radialplate and the other circumferential plates take on gradually chang ingintermediate potentials, or the circumferential plates nearest theradial plate may each be conductively connected to the nearest radialplate.

A pair of conducting vertical slats 71 and 73, and 75 and 77 extendradially on both sides of the arc electrodes 35 and 37. These slats aresuspended from insulating brackets 79 and 81 which are suspended fromthe bases 15 and 17 and are secured to the slats by insulating bolts 83.Conductors 91 and 97 are connected to slats 71 and 77, and to a commonlead through the insert 25, and conductors 93 and 95 are connected toslats 73 and 75 and to a common lead through insert 27, these insertsbeing in the circumferential wall 19 and serve for impressing apotential between the slats. Each. of the slats extends inwardly to apoint very near to the arc electrodes 35 and 37, the edges of the slatsadjacent the rings 45 and 47 extending between the rings. Outwardly, theslats 71, 73, 75, and 77 extend to a region near the cylindricalsections 67 and 69. The slats are mounted just between the two segments61 and 63, and 61' and 63 suspended from each of the bases 15 and 17,respectively.

The chamber 11 is mounted within an electromagnet 101. The north andsouth poles 103 and 105, respectively, extend over the bases 15 and 17,respectively, and are spaced a short distance from the bases.

Actual apparatus with which my invention may be practiced includes avacuum chamber 11 having an ex ternal diameter of about 48 inches andsomewhat less than 3 feet high. This chamber has a volume of about 50cubic feet and is evacuated by a system including a 20-inch oildifiusion pump, an 8-inch oil duffusion booster pump, and a 105 cubicfoot per minute Kinney mechanical pump. The slats have aheight somewhatless than 3 feet and a width somewhat less than 48 inches. The spacingbetween the slats 71, 73, 75, and 77 is about A; inch, and theinsulating brackets 79 and 81 between the slats are of relatively smalldimensions. The magnet has pole faces (103 and 105) which are about, 3feet in diameter and are spaced approximately 3 feet apart. The magnetis 12 /2 feet high, 13 feet long, and 4" feet wide. The iron of themagnet weighs 90 tons, and the magnet is excited by a winding 107 havingcopper coils weighing 11 tons. The magnet is adapted to be excited by2,000 amperes, and when so excited, its flux in the center of the gapbetween the pole faces is about 10,000 gauss.

The energy for the arc is derived from a direct current supply having avoltage of 250 volts, and the current supplied through the arc isusually of the order of 10 amperes throughout most of my experiments,although this current has been as high as amperes, and may be more. Thearc voltage fluctuates between 20 volts and 100 volts.

The arc is fired in the usual manner by bringing the arc electrodes 35and 37 into contact and separating them. For this purpose, a motor (notshown), properly geared to one of the electrodes, usually the anode, isprovided. The movable electrode holder is sealed through a so-calledWilson seal, so that it may be moved backward and forward, and to asmall extent sideways in all directions. The motor is controlled from asuitable thyraton circuit to maintain the arc.

The chamber 11 is grounded. A direct current potential of about 30 voltsis impressed between the rings 45 and 47 and the anode electrode 35. Adirect current potential of about 200 or 300 volts is impressed betweeneach pair of coextensive plates 71 and 75, and 73 and 77, one plate 73and 75 on each side of the arc electrodes being electrically negative,and the other plate 71 and 77 being electrically positive. The supply ofthe potentials between the slats 71 through 77 is insulated from the arepotential supply and the supply of the potential between the positiveelectrode 35 and the rings 45 and 47. Circumferential electric fieldsare, thus, produced between the slats 71 and 75, and 73 and 77.

In operation, the various potentials are impressed be tween the arcelectrodes 35 and 37, the rings 45 and 47 and the positive electrode 35and the slats 71 through 77, and an arc is fired between the arcelectrodes. This are operates between the cathode electrode 37 and theeroded surface 107 (Fig. 3) of the anode electrode 35, producing ions ofthe isotopes to be separated and electrons. Under the action of theelectric field produced between the rings 45 and 47 and the anode arcelectrode 35, and the magnetic field, the ions andv the electrons areprojected into the space in which the circumferential fields areproduced by the slats 71 through 77.

I have found that because of the interaction between the ions and theelectrons, the ions and electrons are projected into the circumferentialfield space in substantially equal numbers per unit volume, and thespacecharge effect of the electrons and the ions is almost completelyneutralized, an extremely small residue giving: the small electric fieldwhich is perpendicular to the magnetic field.

Let us assume that the light ions of mass mi are projected into thecircumferential field space with. a random velocity v1, and the heavyions of mass mz with a random Velocity 1 2, and let v0 be the commonmean radial velocity of these ions, where my may vary slightly from onepoint to another. v0 is somewhat larger than 1 1 or Va. Let V be thepotential impressed between the slats which results in thecircumferential fields. Then there is a radial distance In from thecenter of the are for which V=rrr0voH, where H is the magnetic field,the 'lrvo be ing included because there are two pairs of electrodes. Thecircumferential electric field corresponding to the voltage V is givenby Eo=voH, plus a small electric field due to the random velocities v1and 1 2. Now, if v0 is given, the magnitude which it would have as it isprojected into the space and H a magnitude of the order of 10,000 gauss,the equation V=-zrrovoH may be solved for re assuming V=200 or 300volts, and under the circumstances, it appears that re is equal to thedistance from the center of the arc to a point near the circumferentialremote end of the slat for a vessel of the dimensions described above.

The situation which exists under the above assumptions in thecircumferential field space between slats 73 and 77, where the radialdistance from the arc is less than ro, is illustrated in Fig. 5.Considering for the moment an ion of mass m1 or m2, it is seen that inthis region the force on the ion, by reason of the electric field E, iseE, which would be larger than the force produced by the magnetic fieldHvo, because r is smaller than r0. There would be then a large drift ofthe ions of masses m1 and m2 to the negative slat 73. At the same time,there is a drift of electrons towards the positive slat 77. There isthen the formation of a thin layer of positive space charge upon thenegative slat 73, and the formation of a thin layer of negative spacecharge upon the positive slat 77. The space charges grow in thicknessuntil the electric field is reduced in the vacuum space to a little morethan Eo=Hvo. Thus, in the whole vacuum space, a circumferential electricfield nearly equal to Eo=Hvo exists. Thin space charges at theelectrodes make up the difference between the applied potential, V=7rHvu and the value of E0=Hv0.

The total current among the ions is the ion current flowing to the slat73, and the electron current flowing to 77. There is a force moving thiscurrent outwards, due to the action upon this current of the magneticfield H. This force then is positive for r less than 1'0, and becomeszero at r=ro. For 1' greater than re, the force of this current reversesso that many ions will not get to places where r is greater than re.

The ions are projected into a space in which there is an electric fieldacting circumferentially of intensity approximately E0=Hvo, and if m isthe outer bound of this field, it is subject there to a potential V:roHvo. Now, each cubic centimeter of this space acts difierentially uponthe ions. The lighter ions, as we shall see, are pushed in the directionof the negative electrode, and the heavier ions are pushed in thedirection of the positive electrodes. When they reach the surroundingcylindrical electrode, they deposit out, with the deposit at thepositive end, the richer in heavy ions, and with the deposit at thenegative end the richer in lighter ions.

To understand this, consider the two ions at a given point of the space,with the masses m1 and m2, with the mean velocity of radial motion v0,and the random velocity v1 and v2 in all directions, with m1(vo +v1=m2(vo +v2 and v1 and vz less than vo.

v'ei dt where V'o is the circumferential velocity acquired by the ion inthe time t. Cancelling Hevo against eEo, and integrating Now letting xbe a small radial distance travelled by the ion in time t,

For the gain in the circumferential velocity of the lighter ion on thedistance x,

M 1 1 He 0 w o'l' i 0-1 1 1 O 1 Similarly, for a number of heavy ionswith 1 2 first adding to v0, and then for an equal number with v2opposing w,

and,

be the general value for the field. We get then the equation x He[ 0 1 mflo -U2 Now suppose E adjusts itself so that via, is equal to 0,

as it does very nearly so near the negative electrode.

mm m

Then

He v 0 Her 0 He v -v "W m2 "2 o 2 2 L n 2 2 e 2 On the other hand,suppose E adjusts itself so that vB,=0, as it must approximately do sonear the positive electrode.

1 2 2 2 Then 1) Hev 0 H el v 1 H rog-112 1 1 1 L 0 1 1 L 0 1 1 L 0 1Thus, near the forward edge of the negative plate 73, the field takessuch a value that m1 takes a nearly zero value of total circumferentialvelocity. Then the circumferential velocity of particle m2 will bepositive and equal to 2 o z x On the other hand, near the rear edge ofthe positive plate, the electric field will be of such value that theparticle m2 will have its total circumferential velocity zero. Then thecircumferential velocity of particle m1 will be negative and equal to HeU -v At inbetween points, the motion will be inbetween, the differencein circumferential velocity of the two ions being between H e[v v m -0So far, we have shown that there. is a difference between the twoions,the lighter ions moving toward the negative plate, and the heaviertoward the positive plate. However, we have not given calculableformulae since the x, and the number of ions considered was not known.We will give an experimental figure for uranium ions. For a magneticfield of 6000 gauss, where the radial plates started an inch from thearc, the enrichment of the light isotope found deposited on the firstinch of the plates, with a voltage difference of 7 volts is found to beone-half of one per cent. That is,

and

h n 2m and the interposition of a radial electric field by Larmorstheorem. Of course, for the other ion and the electrons H will not beeliminated. But we see that for such a rotation,

h n 2m and the elimination of the magnetic field, the centrifugal forceis and so we see that it varies as the radius, and, therefore, themotion of the ions will vary as the radius in the original motion.

We have then at a distance r inches from the center,

The V will be 7 r volts. For 20 inches, we will have It is notsurprising that the enrichment increases so rapidly as a function of r.V=1rroHV0 increases proportional to r. But then also the ratio of v1 orvs to V0 is inversely as r, so that we thus get the square of r cominginto the exponential formula in our equations.

The modification of my invention shown in Fig. 7 is similar to thepreferred embodiment of my invention, except that each of the slats 71through 77 is subdivided into a plurality of insulated sections 71athrough 71d through 77a through 77d on which progressively higherpotentials are impressed. In each case, the potentials are such that thefield E is sufiicient to satisfy the requirement that eE is greater thanHevo.

In the modification shown in Fig. 6, the electric cirvc,urrrf ererrtialfield is produced by separate radial slats 201 and 203 at an anglerather than by pairs or sets of slats.

In the, modification shown in Fig. 8, the circumferential electric fieldis produced by impressing potentials of opposite polarity on adjacentsector plates 61 and 63, and 61 and 63. This modification does notinclude radial plates such as 71, 73, 75, 77, or 71a through 77d. Thismodification does include the circumferential plates 67, 69, but theseare omitted in Fig. 8 for clarity.

In the modification shown in Fig. 9, the circumferential plates 67,v 69are omitted and instead there are radial plates 301. These plates 301may be suspended from the end plates 61, 63, 61, 63', the suspensions.being either insulated or conducting. The plates 301 permit theapparatus to be evacuated more readily than plates 67, 69. In addition,the plates 301 facilitate the separation, since uncharged material willpass between them and only charged material will be collected by them.

While I have shown and described certain specific embodiments of myinvention, I am fully aware that many modifications thereof arepossible. My invention, therefore, is not to be restricted exceptinsofar as is necessitated by the spirit of the prior art.

I claim asmy invention:

1. In combination, an arc discharge device including an evacuatedchamber having therein a first electrode and a second electrode, meansfor impressing a potential between said electrodes adequate to producean are therebetween such that said first electrode is electricallynegative relative to said second electrode, and means for impressing amagnetic field coaxial with said electrodes, the said combination beingcharacterized by a first electrode consisting of a conducting materialsurrounding a core of electron emissive material.

2. The combination according to claim 1, wherein the first electrode iscomposed of cored carbon.

3. The combination according to claim 2, wherein the second electrode iscomposed of a uranium containing material.

4. The combination according to claim 1, including means for producingcircumferential fields about the are between the electrodes.

5. The combination according to claim 4, including additional means forproducing an electric field which in the region immediately adjacent thearc is substantially radial with respect to the arc.

6. Apparatus for separating isotopes of a material including means forproducing an are including ions of said isotopes and means forimpressing a magnetic field along said arc, the said apparatus beingcharacterized by means for impressing circumferential electric fieldsabout said arc, each said field being maintained at the same polarity.

7. Apparatus according to claim 6 characterized by the fact that thecircumferential fields are produced by conducting plates extendingradially from the are between which direct current potentials areimpressed.

8. Apparatus according to claim 7 characterized by the fact that theradial dimension of each plate is large compared to the radial distanceof the edge of said plate from the arc.

9. Apparatus according to claim 6 characterized by the fact that thecircumferential fields are produced by a plurality of sets of plateseach set consisting of a plurality of plates extending edge to edgeradially from the arc, said plates being insulated from each other andcorresponding plates of adjacent sets having potentials impressedtherebetween which increase progressively with the radial distance fromthe arc.

10. Apparatus according to claim 9 characterized by the fact that theadjacent edges of successive plates of each set overlap.

11. Apparatus according to claim 9 characterized by the fact that theaggregate radial length of the plates of each set is large compared tothe distance from the are of the edge of the plate adjacent the arc. 1

12. The combination according to claim 1 character ized by the fact thatthe second electrode is composed of a material having a plurality ofisotopes.

for impressing a potential between a pair of adjacent plates on eachsaid side.

14. Apparatus according to claim 13 characterized by the fact that thesegmental plates overlap at their edges.

15. Apparatus according to claim 6 characterized by the fact that spaceof the arc and the circumferential fields is bounded by a plurality ofend-to-end circumferential conducting plates extending in the directionof the magnetic field, said plates being insulated from each other.

16. Apparatus according to claim 6 characterized by the fact that spaceof the arc and the circumferential fields is bounded by a plurality ofradial conducting plates, said plates being insulated from each other.

17. Apparatus according to claim 7 characterized by the fact that thespace of the arc and the radial plates is bounded by a plurality ofend-to-end circumferential conducting plates extending in the directionof the magnetic field, between the outside edges of the radial plates,said plates being insulated from each other.

18. Apparatus according to claim 17 characterized by means connectingthe respective circumferential plates nearest the radial plates to theradial plates to which they are nearest. 7 i

19. Apparatus according to claim 13 characterized by the fact that thespace of the arc and the segmental plates is bounded by a plurality ofend-to-end circumferential conducting plates extending in the directionof the magnetic field, between the outside edges of the segmentalplates, said plates being insulated from each other.

20. Apparatus according to claim 19 characterized by means connectingthe respective circumferential plates :nearest the segmental plates tothe segmental plates to which they are nearest.

21. Apparatus according to claim 6 characterized by the fact that thespace potential with reference to the arc of each point Within the spaceof the circumferential field is substantially proportional to the radialdistance of said point from the arc.

No references cited.

1. IN COMBINATION, AN ARC DISCHARGE DEVICE INCLUDING AN EVACUATEDCHAMBER HAVING THEREIN A FIRST ELECTRODE AND A SECOND ELECTRODE, MEANSFOR IMPRESSING A POTENTIAL BETWEEN SAID ELECTRODES ADEQUATE TO PRODUCEAN ARC THEREBETWEEN SUCH THAT SAID FIRST ELECTRODE IS ELECTRICALLYNEGATIVE RELATIVE TO SAID SECOND ELECTRODE, AND MEANS FOR IMPRESSING AMAGNETIC FIELD COAXIAL WITH SAID ELECTRODES, THE SAID COMBINATION BEINGCHARACTERIZED BY A FIRST ELECTRODE CONSISTING OF A CONDUCTING MATERIALSURROUNDING A CORE OF ELECTRON EMISSIVE MATERIAL.